1. Field of the Invention
The present invention relates to a magnetic transfer device and a magnetic transfer method for transferring preformat information to a magnetic recording layer of a perpendicular magnetic recording medium, the magnetic transfer being carried out by making close contact between a surface of transfer information pattern of a master disk that has a transfer information pattern of ferromagnetic material corresponding to the preformat information to be transferred, and a recording surface of the perpendicular magnetic recording medium that has a magnetic recording layer, and by applying a transferring magnetic field in a direction perpendicular to the surface of close contact.
2. Description of the Related Art
Common hard disk drive (HDD) devices perform recording and reproduction of data by a magnetic head flying over a magnetic recording medium (a hard disk) in a flying height of about 10 nm. Information of bits on the magnetic recording medium is stored on data tracks aligned concentrically. The magnetic head is positioned on the data track to perform recording and reproduction of data. Servo data for the positioning is recorded on the magnetic recording medium. The servo data is recorded on a track concentric to the data track with a predetermined angular interval.
The servo information is generally recorded using a magnetic head. However, a recent increase in recording tracks has caused problems of increase in write time and degradation of efficiency in HDD production.
In order to cope with these problems, a method has been proposed in which the whole of the servo information is collectively recorded on the magnetic recording medium by means of a magnetic transfer technique using a master disk carrying the servo information instead of writing the servo information using a magnetic head.
Japanese Unexamined Patent Application Publication No. 2002-083421 (hereafter, “Patent Document 1”), for example, discloses a method in which a master disk having a servo pattern formed of a ferromagnetic material is used, and preformat information including the servo information on the master disk is transferred to a perpendicular magnetic recording medium
FIG. 7 is a perspective view illustrating a principle of magnetic transfer to a perpendicular magnetic recording medium, with an enlarged view of a conjoined body 300 composed of a master disk 100 and a magnetic recording medium 200 to receive transferred information.
Referring to FIG. 7, a pattern 105 of protrusions and recesses is formed of a ferromagnetic material (preferably a soft magnetic material) on a surface of the master disk 100. The pattern corresponds to preformat information to be transferred. The surface pattern of the master disk 100 is placed into close contact with a recording surface of a magnetic recording medium 200 having a magnetic recording layer 208 to which the information pattern is to be transferred. An external magnetic field 406 as a transferring magnetic field is applied by a magnetic field generating structure 400 having a permanent magnet or the like. Leakage flux 403 penetrates into the medium 200 to generate magnetization 209 in the magnetic recording layer 208 of the medium 200. Thus, magnetic signals along the ferromagnetic pattern 105 on the master disk 100 are transferred to the medium 200.
The magnets composing the magnetic field generating structure 400 are disposed above and under the conjoined body 300 consisting of the master disk 100 and the recording medium 200 adhered with one another, and simultaneously rotated to transfer the whole of the data at once.
Describing the magnetic transfer procedure more in detail, first the surface (a recording surface) of the medium 200 is subjected to a first magnetic field in an approximately perpendicular direction to magnetize the magnetic recording layer 208 of the medium 200 in one direction. Then, the surface of transfer information pattern of the master disk 100 is placed into close contact with the recording surface of the medium 200, and a magnetic field opposite to the first magnetic field is applied.
In this latter step, only a small amount of magnetic flux passes through the recessed parts of the ferromagnetic pattern 105 formed on the master disk 100, leaving a magnetization in the direction of the first magnetic field. The protruding parts of the ferromagnetic pattern 105 allow a large amount of magnetic flux to pass, resulting in magnetization of the protruding parts in the direction of the second magnetic field. As a consequence, a magnetization pattern is transferred corresponding to the protrusions and recesses formed on the surface of transfer information pattern of the master disk 100.
In this way of magnetic transfer, after the transfer process by rotating the magnets of the magnetic field generating structure 400, the magnets must be separated from the conjoined body 300 of the master disk 100 and the medium 200. If the magnets are separated while stopping rotation, the magnetic field becomes non-uniform when the position of the magnets is separated, causing degradation of signals. Japanese Patent No. 3396476 (hereafter, “Patent Document 2”) discloses a method of applying a transfer magnetic field to avoid degradation of transfer signals at the place of separating the magnets by separating the magnets while maintaining the rotation of the magnets.
Japanese Unexamined Patent Application Publication No. 2003-242635 (hereafter, “Patent Document 3”) discloses a magnetic transfer method to obtain good reproduction signals in a slave medium (a medium to receive transferred information) after the transfer process. In the method, magnetic transfer is conducted rotating the slave medium with respect to a magnetic field. After magnetic field application, the slave medium, kept in a rotating state, is moved relative to the magnetic field so that the center of the slave medium separates from the magnetic field in the radial direction. Thus, irregular magnetization in the slave medium is avoided which would occur due to leakage magnetic field of an electromagnet if the rotation is stopped during magnetic field application.
As described above, the magnetic transfer process needs to be carried out while avoiding disturbance to the transfer magnetic field when the magnets are separated. Further, the magnetic field required by magnetic transfer may result in an increase in the size of the magnetic transfer device for perpendicular magnetic recording media.
In the magnetic transfer method as shown in FIG. 7, the magnets need a length extending from the inner periphery to the outer periphery of the medium. A great attractive force acts between the pair of magnets arranged at either side of the medium. As a result, the transfer device needs to strengthen the rigidness of a part for holding the magnet, which leads to a large size of the transfer device.
When the transfer magnetic field is applied while moving the magnets in the radial direction as disclosed in Patent Document 3, the magnets can be short. However, in the case where a transfer magnetic field is applied to a perpendicular magnetic recording medium by a pair of magnets, a pair of magnets simply having a reduced length still generates a diffused leakage flux as shown in FIG. 3, and a transfer magnetic field cannot be applied efficiently.